Lavender (herb) is classed perennial in the cited extension guidance. The timing rules below are relative to your local freeze dates — enter a location to turn them into calendar dates.
The rules this site applies
Method
Frost-relative window
Rule & reconciliation
Transplant outdoors
from the median last spring freeze to 2 weeks after
Utah State University Extension instructs transplanting after the last spring frost, a point rule encoded per policy as a 14-day span opening at the last-frost date; no reconciliation was needed because this is the entry's only source.
No direct-sow outdoors window: Utah State University Extension advises against direct seeding, stating that the germination rate is low and that seeding to transplanting takes between 100 and 200 days.